Re: [RFC PATCH 2/3] ALSA:core: Add rate 24kHz

[Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx>]

On 9/5/19 12:48 AM, Takashi Iwai wrote:
> On Thu, 05 Sep 2019 07:33:00 +0200,
> Pawel Harlozinski wrote:
> > Adds SNDRV_PCM_RATE_24000 at the bottom to keep backward compability
> > with alsa library.
> >
> > Signed-off-by: Pawel Harlozinski <pawel.harlozinski@xxxxxxxxxxxxxxx>
>
> No.  Such a fancy rate has to be handled inside the driver locally
> instead of adding to the common rate.

It's not that crazy, this is supported in the HDaudio spec:

Sample Base Rate Divisor (DIV):
000 = Divide by 1 (48 kHz, 44.1 kHz)
001 = Divide by 2 (24 kHz, 22.05 kHz)

I am not sure why 22.05 made the cut and not 24 kHz, they are both 
derived from common clocks with the same divider... Same for 11.025 and 
12...

> Takashi
>
> > ---
> >   include/sound/pcm.h     | 1 +
> >   sound/core/pcm_native.c | 4 ++--
> >   2 files changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/sound/pcm.h b/include/sound/pcm.h
> > index bbe6eb1ff5d2..09d0a2a2dce8 100644
> > --- a/include/sound/pcm.h
> > +++ b/include/sound/pcm.h
> > @@ -119,6 +119,7 @@ struct snd_pcm_ops {
> >   #define SNDRV_PCM_RATE_192000		(1<<12)		/* 192000Hz */
> >   #define SNDRV_PCM_RATE_352800		(1<<13)		/* 352800Hz */
> >   #define SNDRV_PCM_RATE_384000		(1<<14)		/* 384000Hz */
> > +#define SNDRV_PCM_RATE_24000		(1<<15)		/* 24000Hz */
> >   
> >   #define SNDRV_PCM_RATE_CONTINUOUS	(1<<30)		/* continuous range */
> >   #define SNDRV_PCM_RATE_KNOT		(1<<31)		/* supports more non-continuos rates */
> > diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
> > index 11e653c8aa0e..f52f28e3edb1 100644
> > --- a/sound/core/pcm_native.c
> > +++ b/sound/core/pcm_native.c
> > @@ -2164,13 +2164,13 @@ static int snd_pcm_hw_rule_sample_bits(struct snd_pcm_hw_params *params,
> >   	return snd_interval_refine(hw_param_interval(params, rule->var), &t);
> >   }
> >   
> > -#if SNDRV_PCM_RATE_5512 != 1 << 0 || SNDRV_PCM_RATE_192000 != 1 << 12
> > +#if SNDRV_PCM_RATE_5512 != 1 << 0 || SNDRV_PCM_RATE_192000 != 1 << 12 ||  SNDRV_PCM_RATE_24000 != 1 << 15
> >   #error "Change this table"
> >   #endif
> >   
> >   static const unsigned int rates[] = {
> >   	5512, 8000, 11025, 16000, 22050, 32000, 44100,
> > -	48000, 64000, 88200, 96000, 176400, 192000, 352800, 384000
> > +	48000, 64000, 88200, 96000, 176400, 192000, 352800, 384000, 24000
> >   };
> >   
> >   const struct snd_pcm_hw_constraint_list snd_pcm_known_rates = {
> > --
> > 2.17.1

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